In conventional wet air oxidation, liquor containing oxidizable components is combined with an oxygen containing gas, such as air, and raised to elevated temperatures through both a preheat step in a heat exchanger and by the energy released in oxidation. The effluent, whether vapor or liquid or both, serves as the source of preheat.
Wet air oxidation systems are typically desiigned to operate at a constant reactor temperature.
When the concentration of oxidizable matter in the influent liquor increases, as measured by Chemical Oxygen Demand (COD), further oxidation results in increased heat evolution and a rise in effluent temperature. In conventional heat recovery, the increased effluent temperature will be reflected in an increased influent temperature, thereby aggravating the perturbation from steady state.
Alternately, when the influent liquor COD decreases, diminished heat generation reduces the energy available for preheat exchange and the temperature drop is further amplified.
In a wet air oxidation system having a preheat exchanger of fixed area, and processing influent liquor of variable COD and fouling tendencies, a means of preheat regulation over a wide range of duty and fouling is necessary to prevent detrimental excursions of reactor temperature.